1. Field of the Invention
The present invention relates generally to carrier aggregation (CA) in a heterogeneous network (HetNet), and more particularly, to maximizing a throughput on the heterogeneous network by applying of a plurality of almost blank subframe (ABS) patterns.
2. Description of the Related Art
To increase the coverage and capacity of a macro BS only network, a HetNet is provided, which arranges small cell enhanced nodes B (eNBs) having low power, such as remote radio head (RRH) nodes, pico nodes, femto nodes, and relay nodes in a macro cellular network. The HetNet can improve space re-use effects through cell splitting. However, the HetNet can cause a serious inter-cell interference problem due to a great difference in the transmission (Tx) powers of a macro eNB and a small cell eNB. Accordingly, the HetNet requires new cell association and inter-cell interference coordination (ICIC) technologies for its efficient use. A method has been provided for offloading macro user equipments (UEs) to a small cell eNB and expanding a range of the small cell eNB in order to improve the capacity and fairness of the HetNet.
In order to expand the range of the small cell eNB, a method has also been provided for connecting each UE to a macro eNB or a small cell eNB, sending the greatest downlink (DL) received signal strength (RSS) identically with the macro BS only network, and increasing Tx power of the small cell eNB. However, as a result of this method, UEs located in an expanded area of the small cell eNB and UEs accessed the macro eNB can suffer serious interference.
In order to expand the range of the small cell eNB, another method has been provided for giving a positive offset (i.e., a range expansion bias) to DL RSS of a small cell eNB and enabling UEs receiving greater DL RSS from a macro eNB but being located closer to the small cell eNB to be connected to the small cell eNB. This method expands the range of the small cell eNB without increasing Tx power of the small cell eNB. However, as a result of this method UEs located in an expanded area of the small cell eNB, specifically, UEs accessing the small cell eNB suffer serious inter-cell interference from the macro eNB sending stronger DL RSS than the small cell eNB. Thus, when a macro UE is located in a boundary of a macro cell, the range expansion of the small cell eNB can improve the capacity of the macro cell due to offloading of the macro UE to the small cell eNB. However, when a small cell UE is located in a range expansion area of the small cell eNB, the range expansion of the small cell eNB can deteriorate overall sum capacity due to the low link performance of the small cell UE. Also, the macro UEs cannot be serviced at a macro ABS pattern for small cell range expansion.